Background will not get called unless and until the Dial application fails, and, in any case will only produce output on the channel on which it is being run. If Dial gets answered, it continues to run until one side hangs up, and only if the g option is used and it is the called party that hangs up, will it run the next “priority”. As the called party is hungup at this stage, the next priority cannot do anything to the called party.
Background is interruptible by DTMF; you would normally use Playback.
I think that you have so many misunderstandings of how Asterisk works that you need to read the documentation again, or employ someone else to configure it for you.
(Dial has options to play recordings on called channels.)